1. Field of the Invention
The present invention relates to an apparatus for electrical function checking of wiring matrices in which gas discharges in gas discharge channels provide ionic contacting.
2. Description of the Prior Art
In automatic testing units and test adaptors for unequipped and equipped printed circuit boards, as well as for wiring matrices which are prepared by soldering or crimping, the contacting of selected measuring locations thereon is usually undertaken using resilient test probes. The resilient test probes are arranged in a grid having the dimensions of the wiring matrix to be tested and are secured by resilient sleeves which are pressed into a carrier platen and into which the test probes are pushed. The dimensions of the test probes are selected to have the smallest spacing of the measuring locations relative to one another, as well as having sufficient diameter to carry the current load required. In the publication Elektronik Produktion und Pruftechnik, November 1979, pp. 472 and 483, 0.69 mm is generally cited as a lower limit for the diameter of such probes.
For the known function checking apparatus for circuit boards, tests on conductivity and insulation measurements are performed between test locations formed by grid points in accordance with the layout of the circuit board. Since the resilient test probes for contacting the test locations must be arranged in the grid of the printed circuit, the realization of such test apparatus becomes increasingly difficult as the grid dimensions decrease and the areas of the printed circuit boards increase. Thus, an arrangement of resilient test probes in grid dimensions of below 1 mm can generally not be precisely engineered to give a reliable mechanical contacting with the test locations. With the increasing number of test locations, which can, for example, amount to over 100,000 test locations, the number of leads and switch elements required also increases. This causes a considerable apparatus oriented outlay and correspondingly higher costs. Moreover, the probability of completely contacting the printed circuit boards considerably decreases for the increased number of measuring locations.
European Pat. No. A-0 102 565 discloses an apparatus for electrical function checking of wiring matrices wherein standard ohmic contacts are replaced by non-touching ionic contacts through gas discharge paths. A plurality of gas discharge channels are provided with electrodes and extend into a carrier plate for placement over the wiring matrix. The gas discharge channels are arranged in a framework similar to the wiring matrix and are open toward the measuring locations on the matrix. When two selected measuring locations are connected to one another in an electrically conductive fashion, such as by an interconnect, the corresponding gas discharge channels form two series connected gas discharge paths which can be triggered by applying an adequately high voltage to the respective electrodes. A current flow then ensues upon the ignition of the gas discharges and can be measured for test purposes. When the ignition of the gas discharge does not occur, or when the current flow is lower than is expected after ignition, then conclusions can be drawn regarding an interrupted connection between the selected measuring locations, including that an electrically conductive connection did not exist at all.
When an AC voltage is superimposed over the voltage supplied to the electrodes, then the phase of the resulting current change is compared to the phase of the AC voltage to identify the impedance of the connection between the selected measuring locations.
Thus, the known devices enable conductivity and insulation measurements to be performed with extremely high reliability by avoiding ohmic contacts. Using such ionic contacting of the measuring locations through gas discharge channels, extremely small dimensions can be realized. Wiring matrices having grid dimensions of the measuring locations of down to 0.1 mm can be tested reliably using such devices. Given the high number of test locations for a wiring matrix to be tested, however, problems continue to occur. Such problems arise as a result of the numerous leads and test elements required for connection of the electrodes in the gas discharge channels.
Use of laser beams for labelling is disclosed in Laser 79 Opto-Electronics, Vol. 2 through 6, July 1979, pp. 235-239.